Midsole Structure for an Athletic Shoe

ABSTRACT

The midsole structure for an athletic shoe includes a midsole body made of foamed resin, and a sheet composite extending at least from the ball of the foot portion to the toe portion in the midsole body and comprising a plurality of foamed rubber sheets that are overlapped and shifted in the longitudinal direction. The sheet composite comprises a single sheet at the toe portion and a plurality of sheets at the ball of the foot portion.

BACKGROUND OF THE INVENTION

The present invention relates generally to a midsole structure for anathletic shoe, and more particularly, to an improvement in the midsolestructure so as to improve cushioning property and a touch on a foot ofa shoe wearer and enhance a propulsion force during exercises.

Japanese patent application publication No. 2001-149101 discloses a solestructure for a boot. The sole includes a rubber sole body, a corematerial disposed above the sole body and made of foamed rubber, and arubber-made shape-keeping material sandwiched between the sole body andthe core material. The publication describes that a favorable cushioningproperty can be exhibited by the relatively thick core material made offoamed rubber and rigidity can be improved by the rubber-madeshape-keeping material (see paras. [0018] to [0022], FIG. 1).

In athletic shoes such as running shoes and the like, since a solethickness of a toe is thin, it is difficult to insert the relativelythick core material (or insole board) made of foamed rubber according tothe prior art into a tip end of the toe. On the other hand, in the casethat the sole thickness of the toe is made thick such that the insoleboard can be inserted into the tip end of the toe, cushioning propertyof the other sole regions maybe decreased. Also, in the prior-artstructure, since the rubber sole body is used, there is a deficiencythat the weight of the entire sole is heavy.

The present invention has been made in view of these circumstances andits object is to provide a midsole structure for an athletic shoe thatcan improve cushioning property and a touch on a foot of a shoe wearerand that can enhance a propulsion force during exercises. Also, thepresent invention is directed to decreasing the weight of such a midsolestructure.

Other objects and advantages of the present invention will be obviousand appear hereinafter.

SUMMARY OF THE INVENTION

A midsole structure for an athletic shoe according to one aspect of thepresent invention includes a midsole body made of foamed synthetic resinand a sheet composite extending at least from a ball of a foot portionto a toe portion in the midsole body and comprising a plurality offoamed rubber sheets that are overlapped and shifted in a longitudinaldirection. The sheet composite includes a single sheet at the toeportion and a plurality of sheets at the ball of the foot portion.

According to the present invention, at the ball of the foot portion ofthe midsole body, a plurality of foamed rubber sheets of the sheetcomposite, that is, a thick sheet layer made of foamed rubber isdisposed. Therefore, a touch on a foot of a wearer can be improved atthe ball of the foot portion and cushioning property can be enhanced atthe ball of the foot portion.

At the toe portion of the midsole body, a single foamed rubber sheet ofthe sheet composite, that is, a thin sheet layer made of foamed rubberis disposed. Thereby, as a load at the time of impacting the ground istransferred from the ball of the foot portion to the toe portion, adownward sinking movement of the foot is gradually decreased. During apush-off motion of the foot at the toe portion, a high repellent forcecan be obtained and thus a propulsion force during exercises can beincreased. Moreover, according to the present invention, since themidfoot body is made of foamed resin, the total weight of the midsolestructure can be reduced.

The midsole body may include a stepped concave portion that is open to afoot-sole-contact-surface side and that has a difference in level in thelongitudinal direction. The sheet composite may be housed in such aconcave portion. In this case, at a deeper concave portion, a pluralityof sheets of the sheet composite are disposed and at a shallower concaveportion, a single sheet of the sheet composite is disposed.

The midsole body may include a stepped concave portion that is open to aground-contact-surface side and that has a difference in level in thelongitudinal direction. The sheet composite may be housed in such aconcave portion. In this case as well, at a deeper concave portion, aplurality of sheets of the sheet composite are disposed and at ashallower concave portion, a single sheet of the sheet composite isdisposed.

The midsole body may include a stepped concave portion that passesthrough the midsole body in a thickness direction and that has adifference in level in the longitudinal direction. The sheet compositemay be housed in such a concave portion. In this case too, at a deeperconcave portion, a plurality of sheets of the sheet composite aredisposed and at a shallower concave portion, a single sheet of the sheetcomposite is disposed.

The midsole body may include a stepped inner space that has a differencein level in the longitudinal direction. The sheet composite may behoused in such an inner space. In this case as well, at a deeper innerspace, a plurality of sheets of the sheet composite are disposed and ata shallower inner space, a single sheet of the sheet composite isdisposed.

The sheet composite may be disposed at a forefoot portion, or a heelportion of said midsole body. Alternatively, the sheet composite mayextend from the heel portion through a midfoot portion to the forefootportion of the midsole body. In either case, at a region where the sheetcomposite comprises a plurality of sheets, a touch on the foot of thewearer and cushioning property can be improved by the thick sheet layermade of foamed rubber, whereas at a region where the sheet compositecomprises a single sheet, a high repellent force can be obtained and apropulsion force can thus be increased by the thin sheet layer made offoamed rubber.

The sheet composite disposed at the heel portion of the midsole body maybe separated from the sheet composite disposed at the forefoot portionof the midsole body in the longitudinal direction.

A midsole structure for an athletic shoe according to another aspect ofthe present invention includes a midsole body made of foamed syntheticresin and a sheet composite extending at least from a ball of a footportion to a toe portion in the midsole body and comprising a firstsheet and a second sheet that are made of foamed rubber and that areoverlapped and shifted in the longitudinal direction. Each of the firstsheet and the second sheet has a front end disposed on a front sidethereof and a rear end disposed on a rear side thereof in thelongitudinal direction. The front end of the first sheet is located infront of the front end of the second sheet at the toe portion of themidsole body.

According to the present invention, at the ball of the foot portion ofthe midsole body, the first and second foamed rubber sheets of the sheetcomposite, that is, a thick sheet layer made of foamed rubber isdisposed. Therefore, a touch on a foot of a wearer can be improved atthe ball of the foot portion and cushioning property can be enhanced.

At the toe portion of the midsole body, the first foamed rubber sheet ofthe sheet composite, that is, a thin sheet layer made of foamed rubberis disposed. Thereby, as a load at the time of impacting the ground istransferred from the ball of the foot portion to the toe portion, adownward sinking movement of the foot is gradually decreased. Also,during a push-off motion of the foot at the toe portion, a highrepellent force can be obtained and thus a propulsion force duringexercises can be increased. Moreover, according to the presentinvention, since the midfoot body is made of foamed resin, the totalweight of the midsole structure can be reduced.

The front end of the first sheet may contact the midsole body fromabove. Thereby, during the push-off motion of the foot at the toeportion, a greater repellent force can be obtained.

The rear end of the first sheet may extend to the rear of the rear endof the second sheet. Thereby, as a load is transferred from the rear endof the first sheet through the rear end of the second sheet to anoverlapped region of the first and second sheets, cushioning propertyand a touch on the foot of the wearer can be gradually improved.

The first sheet may be disposed at a forefoot portion and a heel portionof the midsole body and the second midsole may comprise a forefoot sheetportion disposed at the forefoot portion of the midsole body and a heelsheet portion disposed at the heel portion of the midsole body. Theforefoot sheet portion and the heel sheet portion may be separated fromeach other in the longitudinal direction.

In this case, at a region where the first and second sheets areoverlapped with each other, a touch on the foot of the wearer andcushioning property can be improved by a thick sheet layer made offoamed rubber, whereas at a region where only the first sheet isdisposed, a high repellent force can be obtained and a propulsion forcecan be increased by a thin sheet layer made of foamed rubber.

As explained above, according to the midsole structure of the presentinvention, since a plurality of foamed rubber sheets of the sheetcomposite, that is, a thick sheet layer made of foamed rubber isdisposed at the ball of the foot portion of the midsole body, a touch ona foot of a wearer can be improved and cushioning property can beenhanced at the ball of the foot portion. Also, since a single foamedrubber sheet of the sheet composite, that is, a thin sheet layer made offoamed rubber is disposed at the toe portion of the midsole body, duringa push-off motion of the foot at the toe portion, a high repellent forcecan be obtained and thus a propulsion force during exercises can beincreased. Moreover, since the midfoot body is made of foamed resin, thetotal weight of the midsole structure can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference should bemade to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention.

FIG. 1 is a top plan schematic view of a midsole structure for anathletic shoe according to a first embodiment of the present invention.

FIG. 2 is a sectional view of FIG. 1 taken along line II-II illustratinga longitudinal sectional view along a longitudinal centerline of themidsole structure of FIG. 1.

FIG. 3 is a cross sectional view of FIG. 1 taken along line.

FIG. 4 is a cross sectional view of FIG. 1 taken along line IV-IV.

FIG. 5 is a top plan schematic view of a midsole structure for anathletic shoe according to a second embodiment of the present invention.

FIG. 6 is a sectional view of FIG. 5 taken along line VI-VI illustratinga longitudinal sectional view along a longitudinal centerline of themidsole structure of FIG. 5.

FIG. 7 is a cross sectional view of FIG. 5 taken along line VII-VII.

FIG. 8 is a cross sectional view of FIG. 5 taken along line VIII-VIII.

FIG. 9 is a top plan schematic view of a midsole structure for anathletic shoe according to a third embodiment of the present invention.

FIG. 10 is a sectional view of FIG. 9 taken along line X-X illustratinga longitudinal sectional view along a longitudinal centerline of themidsole structure of FIG. 9.

FIG. 11 is a cross sectional view of FIG. 9 taken along line XI-XI.

FIG. 12 is a cross sectional view of FIG. 9 taken along line XII-XII.

FIG. 13 is a top plan schematic view of a midsole structure for anathletic shoe according to a fourth embodiment of the present invention.

FIG. 14 is a sectional view of FIG. 13 taken along line XIV-XIVillustrating a longitudinal sectional view along a longitudinalcenterline of the midsole structure of FIG. 13.

FIG. 15 is a cross sectional view of FIG. 13 taken along line XV-XV.

FIG. 16 is a cross sectional view of FIG. 13 taken along line XVI-XVI.

FIG. 17 is a top plan schematic view of a midsole structure for anathletic shoe according to a fifth embodiment of the present invention.

FIG. 18 is a sectional view of FIG. 17 taken along line XVIII-XVIIIillustrating a longitudinal sectional view along a longitudinalcenterline of the midsole structure of FIG. 17.

FIG. 19 is a cross sectional view of FIG. 17 taken along line XIX-XIX.

FIG. 20 is a cross sectional view of FIG. 17 taken along line XX-XX.

FIG. 21 is a top plan schematic view of a midsole structure for anathletic shoe according to a sixth embodiment of the present invention.

FIG. 22 is a sectional view of FIG. 21 taken along line XXII-XXIIillustrating a longitudinal sectional view along a longitudinalcenterline of the midsole structure of FIG. 21.

FIG. 23 is a cross sectional view of FIG. 21 taken along lineXXIII-XXIII.

FIG. 24 is a cross sectional view of FIG. 21 taken along line XXIV-XXIV.

FIG. 25 is a top plan schematic view of a midsole structure for anathletic shoe according to a seventh embodiment of the presentinvention.

FIG. 26 is a sectional view of FIG. 25 taken along line XXVI-XXVIillustrating a longitudinal sectional view along a longitudinalcenterline of the midsole structure of FIG. 25.

FIG. 27 is a cross sectional view of FIG. 25 taken along lineXXVII-XXVII.

FIG. 28 is a cross sectional view of FIG. 25 taken along lineXXVIII-XXVIII.

FIG. 29 is a top plan schematic view of a midsole structure for anathletic shoe according to an eighth embodiment of the presentinvention.

FIG. 30 is a sectional view of FIG. 29 taken along line XXX-XXXillustrating a longitudinal sectional view along a longitudinalcenterline of the midsole structure of FIG. 29.

FIG. 31 is a cross sectional view of FIG. 29 taken along line XXXI-XXXI.

FIG. 32 is a cross sectional view of FIG. 29 taken along lineXXXII-XXXII.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toembodiments thereof as illustrated in the accompanying drawings. Here, arunning shoe is taken for an example as an athletic shoe.

In the following explanation, “upward (upper side/upper)” and “downward(lower side/lower)” designate an upward direction and a downwarddirection, or vertical direction, of the shoe, respectively, “forward(front side/front)” and “rearward (rear side/rear)” designate a forwarddirection and a rearward direction, or longitudinal direction, of theshoe, respectively, and “a width(or lateral) direction” designates acrosswise direction of the shoe.

For example, in FIG. 1, a top plan schematic view of the midsolestructure of the shoe, “upward” and “downward” designate “out of thepage” and “into the page” in FIG. 1, respectively, “forward” and“rearward” designate “upward” and “downward” of FIG. 1, respectively,and “a width direction” designates “left to right direction” in FIG. 1.

Also, in FIG. 2, a longitudinal sectional view and in FIGS. 3, 4, crosssectional views, only the sheet composite constituting the midsolestructure according to the present embodiment is shown by hatching andhatching of a midsole body and an outsole is omitted for illustrationpurposes. In the drawings, reference characters H, M and F designate aheel region, a midfoot region and a forefoot region of the midsolestructure, respectively, which are adapted to correspond to a heelportion, a midfoot portion or a plantar arch portion and a forefootportion of a foot of a shoe wearer, respectively.

First Embodiment

FIGS. 1 to 4 show a midsole structure for an athletic shoe according toa first embodiment of the present invention. As shown in FIGS. 1 and 2,the midsole structure 1 includes a midsole body 2 extending from theheel region H through the midfoot region M to the forefoot region H anda sheet composite (see hatched portions) 3 extending from the heelregion H through the midfoot region M to the forefoot region H on a sideof an upper surface (i.e. a foot-sole-contact-side surface) 20 of themidsole body 2. On a lower surface (i.e. a ground-contact-side surface)22 of the midsole body 2, an outsole 4 is fixedly attached that has aground-contact surface that contacts the ground. As shown in FIGS. 2 to4, the midsole body 2 has an upraised portion 21 that extends upwardlyfrom an outer circumferential edge portion of the upper surface 20. Abottom portion of an upper (not shown) of the shoe is to be fixedlyattached to the upraised portion 21. In such a manner, the athletic shoeis assembled.

As shown in FIGS. 1 to 4, the upper surface 20 of the midsole body 2 hasconcave portions or concavities 2A, 2B formed therein to house the sheetcomposite 3. The concave portion 2A disposed on an upper side is open tothe upper surface 20, and the concave portion 2B disposed on a lowerside is open to the upper surface 20 through the concave portion 2A.None of the concave portions 2A, 2B are not open to the lower surface 22of the midsole body 2.

A front-end wall portion 2A₁ of the concave portion 2A is located infront of a front-end wall portion 2B₁ of the concave portion 2B. Arear-end wall portion 2A₂ of the concave portion 2A is located at therear of a rear-end wall portion 2B₂ of the concave portion 2B. Agenerally longitudinal length of the concave portion 2A is longer thanthat of the concave portion 2B. Thereby, between the concave portions 2Aand 2B, there is formed a stepped surface 2Ab₁ at the forefoot region Fand a stepped surface 2Ab₂ at the heel region H. Also, sidewall portionsof the concave portions 2A, 2B have no stepped surfaces and are alignedwith each other in the lateral direction (see FIGS. 1 to 3) and thus thesidewall portions of the concave portions 2A, 2B have straight surfacesin the vertical direction (see FIGS. 3, 4).

The sheet composite 3 comprises an upper sheet (or a first sheet) 30disposed on an upper side and a lower sheet (or a second sheet) 31disposed on a lower side. The upper sheet 30 is housed in the concaveportion 2A and the lower sheet 31 is housed in the concave portion 2B. Alower surface 31B of the lower sheet 31 is fitted on a bottom wallsurface 2B₀ of the concave portion 2B, a front end 31 a of the lowersheet 31 faces the front-end wall portion 2B₁ of the concave portion 2B,and a rear end 31 b of the lower sheet 31 faces the rear-end wallportion 2B₂ of the concave portion 2B. A lower surface 30B of the uppersheet 30 is fitted on an upper surface 31A of the lower sheet 31, afront end 30 a of the upper sheet 30 faces the front-end wall portion2A₁ of the concave portion 2A, and a rear end 30 b of the upper sheet 30faces the rear-end wall portion 2A₂ of the concave portion 2A. An uppersurface 30A of the upper sheet 30 forms a foot-sole-contact-sidesurface, which follows a contour of the foot of the wearer.

The sheet composite 3 has a two-layer structure at a region in which theupper and lower sheets 30, 31 are overlapped with each other, and thesheet composite 3 has a single-layer structure with only the upper sheet30 at regions ahead of the lower sheet 31 and behind the lower sheet 31,i.e. at regions of the stepped surfaces 2Ab₁ and 2Ab₂. That is to say,the front end 30 a of the upper sheet 30 is disposed in front of thefront end 31 a of the lower sheet 31 and the rear end 30 b of the uppersheet 30 is disposed at the rear of the rear end 31 b of the lower sheet31. In other words, the sheet composite 3 is so structured as to overlapthe upper sheet 30 and the lower sheet 31 with the front and rear ends30 a, 30 b of the upper sheet 30 shifted relative to the front and rearends 31 a, 31 b of the lower sheet 31.

As shown in FIGS. 2 to 4, the upper sheet 30 has a uniform thickness inthe longitudinal direction as well as in the lateral direction. Thelower sheet 31 also has a uniform thickness in the longitudinaldirection as well as in the lateral direction. In this example, thethickness of the upper sheet 30 is the same as the thickness of thelower sheet 31. The sidewalls of the upper sheet 30 are generallyperpendicular to the upper surface 30A and the lower surface 30B. thesidewalls of the lower sheet 31 are also generally perpendicular to theupper surface 31A and the lower surface 31B.

As shown in FIG. 2, the thickness of the two-layer-structure portion ofthe sheet composite 3 relative to the midsole structure 1 occupiesapproximately half of the thickness of the midsole structure 1 at theheel region H, more than half of the thickness of the midsole structure1 at a region from the midfoot region M to the forefoot region F, andthe occupied thickness ratio gradually increases toward the toe of thefoot. On the other hand, the thickness of a single layer portion of thesheet composite 3 relative to the midsole structure 1 occupies a verysmall part of the thickness of the midsole structure 1 at the heelregion H, and the occupied thickness ratio in the forefoot region Fgradually increases toward the toe of the foot.

As shown in a bone structure of the foot described in FIG. 1, the frontend 30 a of the upper sheet 30 extends to a position of a proximalportion of a distal phalanx DP₁ of a first toe, and the front end 31 aof the lower sheet 31 extends to a position of a proximal portion of aproximal phalanx PP₁ of the first toe. Therefore, a thenar eminenceportion or a ball of the foot TE, which includes a metatarsophalangealjoint MJ₁ between the proximal phalanx PP₁ and a metatarsus MB₁ of thefirst toe and a bulged portion around the metatarsophalangeal joint MJ₁,is located at a region of the two-layer structure composed of theoverlapped upper and lower sheets 30, 31.

The toe portion of the foot that includes a distal end portion of theproximal phalanx PP₁ of the first toe and the proximal portion of thedistal phalanx DP₁ of the first toe is located at a region of asingle-layer structure composed of only the upper sheet 30. The sheetcomposite 3 of the present embodiment extends from at least the ball ofthe foot portion TE to the toe. As shown in FIG. 2, the thickness of themidsole body 2 at the forefoot region F becomes gradually thinner towardthe tip of the toe. A reference numeral 2 e in FIG. 2 designates thethinnest portion of the midsole body 2 disposed between a foremost endof the stepped surface 2Ab₁ of the midsole body 2 and the lower surface22 of the midsole body 2.

The midsole body 2 is formed of a foamed synthetic resin, moreparticularly, foamed thermoplastic resin such as foamed ethylene-vinylacetate copolymer (EVA) and the like, or foamed thermosetting resin suchas foamed polyurethane (PU) and the like. The sheet composite 3 isformed of foamed rubber, more particularly, foamed body of naturalrubber, isoprene rubber, butadiene rubber, styrene butadiene rubber,nitrile butadiene rubber or the like. The hardness of the midsole body 2is set at for example 50 to 60 C in Asker C hardness scale and thehardness of the sheet composite 3 is set at for example 10 to 40 C inAsker C hardness scale. As the sheet composite 3, a material of a lowhardness and high repulsion is preferable. The outsole 4 is preferablyformed of a harder elastic material than the midsole body 2, morespecifically, thermoplastic resin such as ethylene-vinyl acetatecopolymer (EVA) and the like, thermosetting resin such as polyurethane(PU) and the like, or rubber material such as butadiene rubber,chloroprene rubber and the like. The hardness of the outsole 5 is set atfor example 50 to 90 A in Asker A hardness scale.

The, we will provide an additional explanation of the rubber foam thatconstitutes the sheet composite 3.

The rubber foam used in the present embodiment is formed of foamingrubber composition that includes rubber composition and foaming agent.The rubber foam is crosslinked foam in which the rubber composition iscrosslinked and foamed.

The rubber composition is composed of at least one of either naturalrubber or synthetic rubber. As synthetic rubber, isoprene rubber,butadiene rubber, styrene butadiene rubber may be used. 1 kind in theserubbers may be solely used, alternatively, 2 or more kinds in theserubbers may be used together. Natural rubber and synthetic rubber may beused together. The content of the rubber composition relative to theentire rubber foam is preferably 40 to 90% by mass. That is because inthe case of less than 40% by mass maintenance of repellant elasticitybecomes difficult and in the case of more than 90% by mass processingsometimes becomes difficult due to occurrence of a crack during forming.

In addition, when using at least one of either natural rubber orisoprene rubber, the total content of the natural rubber and isoprenerubber relative to the entire rubber composition (i.e. total mass of therubber composition) is preferably 60 to 100% by mass. That is because inthe case of less than 60% by mass repellant elasticity cannot bemaintained and processability or workability is deteriorated. Rubbercomposition is preferably mixed with nitrile butadiene rubber. Becausenitrile group of nitrile butadiene rubber has polarity oil resistance ofthe rubber foam can be improved.

Foaming agents are not particularly limited if only it can generate gasnecessary for foaming rubber composition by heating. 1 kind solely, or 2kinds or more in combination may be used. The content of the foamingagents relative to the entire rubber composition is preferably 0.5 to10% by mass, more preferably 2 to 5% by mass. That is because in thecase of less than 0.5% by mass it is sometimes hard to foam stably andin the case of more than 10% by mass a problem occurs that the diameterof superficial or internal foamed cell varies due to excess-foaming.

The rubber foam according to the present embodiment is so formed as toadd crosslinking agents, crosslinking assistant, foaming auxiliaryagents, vulcanization accelerator, processing aid, reinforcing agentsand the like to the above-mentioned rubber composite to crosslink andfoam under a predetermined condition.

The crosslinking agents are not particularly limited, but sulfur that iscommon as crosslinking agents for rubber and organic peroxide thatpromotes peroxide crosslinking are used. These may be used by 1 kindsolely, or by 2 kinds or more in combination. The content of thecrosslinking agents relative to the entire rubber composite ispreferably 1 to 7% by mass, more preferably 2 to 5% by mass. That isbecause in the case of less than 1% by mass repellent elasticitysometimes decreases due to an inadequate cross linking and in the caseof more than 7% by mass foaming is sometimes inadequately performed dueto an excessive crosslinking.

The crosslinking assistant is not particularly limited, but it may beused by 1 kind solely, or by 2 kinds or more in combination. The contentof the crosslinking assistant relative to the entire rubber composite ispreferably 1 to 10% by mass, more preferably 3 to 5% by mass. That isbecause in the case of less than 1% by mass repellent elasticitysometimes decreases due to an inadequate cross linking and in the caseof more than 10% by mass weight reduction of a product becomes sometimeshard due to a great specific gravity of the rubber composite.

Foaming auxiliary agents are not particularly limited, but ureacompound, zinc compound and the like may be used. These may be used by 1kind solely, or by 2 kinds or more in combination. The content of thefoaming auxiliary agents relative to the entire rubber composite ispreferably 0.5 to 10% by mass. The foaming auxiliary agents are normallyequal in quantity to the foaming agents. In the case that an addition ofthe foaming agents is less than an addition of the foaming auxiliaryagents, some of the foaming agents produce formaldehyde or the like.Therefore, suitable adjustment is required according to the amount ofaddition of the foaming agents.

Vulcanization accelerator is not particularly limited, but it may beused by 1 kind solely, or by 2 kinds or more in combination. The contentof the vulcanization accelerator relative to the entire rubber compositeis preferably 0.2 to 3% by mass. That is because in the case of lessthan 0.2% by mass molding needs a long time to decrease productivity andrepellent elasticity decreases due to an inadequate cross linking and inthe case of more than 3% by mass the probability of blooming in themolding becomes higher.

From the point of improvement in fluidity and lubricity of rubbercomposite, restraint for attachment to kneading machines such asrollers, and improvement of mold-releasing effect, the content ofprocessing aid relative to the entire rubber foam that may includeprocessing aid is preferably 0 to 2% by mass. That is because in thecase of more than 2% by mass rollers may slip relative to materials dueto too greater lubricity and thus materials may become hard to be mixedat the time of processing rollers.

From the point of improvement in mechanical property such as tensilestrength, wear resistance and the like of vulcanized rubber, rubber foammay contain reinforcing agents. The content of reinforcing agentsrelative to the entire rubber composite is preferably 5 to 50% by mass.That is because in the case of less than 5% by mass adequate strengthmay not be obtained and in the case of more than 50% by mass repellentelasticity may be deteriorated and specific gravity of the foam maybecome too great.

Then, a manufacturing method of rubber foam will be briefly explained.

Firstly, materials such as a rubber composition as a base material, acrosslinking agent and a foaming agent are casted into the kneadingmachine. By kneading these materials, a foaming rubber composition ismanufacture (kneading process). In this case, rubber compositions,crosslinking aids, reinforcement agents, crosslinking agents,vulcanizing accelerators, foaming auxiliary and foaming agents arecasted in this order into rollers heated to a predetermined temperature(for example, the surface temperature is 40-60° C.), and are kneaded.Thereafter, preforming such as sheeting and pelletizing is performed.

Secondly, the foaming rubber composite acquired in the kneading processis inserted into a metal mold and a heating process is conducted topromote foaming by the foaming agents. Thereafter, by performing aforming process and a mold-releasing process, a foaming rubbercomposition having a desired shape (foam molding process). In this case,the heating temperature in the heating process differs depending on thekinds of foaming agents and foaming aids, but the heating process isperformed at a decomposition temperature or more (for example, 120-180°C.) of the foaming agents that are used.

The coefficient of repellant or rebounding elasticity or impactresilience coefficient of the rubber foam that was manufactured in theabove-mentioned process is 72-84% according to the measurement methodbased on ASTM-D2632. In contrast, the impact resilience coefficient ofan EVA foam of a high impact resilience is 63% according to the samemethod. The impact resilience coefficient of the rubber foam used inthis embodiment has been found to be improved by 14-33% relative to theEVA of a high impact resilience. In the specific measurement, a foamsample (thickness: 10±1 mm) is prepared and VERTICAL REBOUND RESILIENCETESTER_GT-7042-V of GOTECH is used. At the environmental temperature(23±3° C.), a metal plunger is dropped eight times at every 5 seconds.During five times in the later half, the indicator (%) at the standstillpoint (i.e. the rebounding height) of the metallic plunger after eachrebounding is read and its average value is made the coefficient ofrebounding elasticity.

In the midsole structure 1 structured as above-mentioned, when a load atthe time of impacting the ground is transferred to the ball of the footportion TE of the midsole body 2 during exercises, thetwo-layer-structured sheet composite 3 composed of upper and lowersheets 30, 31 made of foamed rubber, that is, a thick foamed-rubbersheet layer is disposed at the ball of the foot portion TE. Thereby, atouch on the foot of the wearer can be improved and cushioning propertycan be enhanced at the ball of the foot portion TE.

Next, when the load is transferred to the toe portion, a single-layeredsheet composite 3 composed of only the upper sheet 30 made of foamedrubber, that is, a thin foamed-rubber sheet layer is disposed at the toeportion. Thereby, as the load on landing moves from the ball of the footportion TE to the toe portion, a downward sinking movement of the footis gradually lessened, a high repellent force can be obtained at thetime of a push-off motion of the toe portion, and a propulsive force canthus be increased during exercises.

Especially, in the present embodiment, the thin portion 2 e of themidsole body 2 is formed between the frontmost end portion of thestepped surface 2Ab₁ of the midsole body 2 and the lower surface 22 ofthe midsole body 2. Therefore, when the foot pushes off at the toeportion on the stepped surface 2Ab₁, a higher repellent force againstthe push-off force of the foot can be obtained from the stepped surface2Ab₁. As a result, a higher propulsive force can be attained. Also, asfoamed rubber composing the sheet composite 3, if the above-mentionedhigh rebounding rubber foam is used, a still higher rebounding force canbe obtained and a much greater propulsive force can be attained. Inaddition, since the midsole body 2 is formed of foamed rubber, theentire weight of the midsole structure can be reduced.

Also, when the wearer impacts the ground at a heel rear end duringexercises and the load is transferred from the heel rear end to a heelcenter, the load moves from a single-layer region to the double-layerregion of the sheet composite 3. Thereby, a touch on the foot andcushioning property are improved gradually or in stages.

Second Embodiment

FIGS. 5 to 8 show a midsole structure for an athletic shoe according toa second embodiment of the present invention. In these drawings, likereference numbers indicate identical or functionally similar elements tothose in the first embodiment. In the first embodiment, an example wasshown in which the concave portions 2A, 2B that house the sheetcomposite 3 are formed on the upper surface (i.e. thefoot-sole-contact-side surface) 20 of the midsole body 2. In this secondembodiment, the concave portions 2A, 2B that house the sheet composite 3are formed on the lower surface (i.e. the ground-contact-side surface)22 of the midsole body 2.

That is, the concave portion 2B disposed below is open to the lowersurface 22 and the concave portion 2A disposed above is open to thelower surface 22 through the concave portion 2B. Neither of the concaveportions 2A, 2B are not open to the upper surface 20.

Also, generally longitudinal lengths of the upper sheet 30 and the lowersheet 31 that constitute the sheet composite 3 of this second embodimentare opposite to generally longitudinal lengths of the upper sheet 30 andthe lower sheet 31 that constitute the sheet composite 3 of the firstembodiment. That is, the front end 30 a of the upper sheet 30 isdisposed at the rear of the front end 31 a of the lower sheet 31 and therear end 30 b of the upper sheet 30 is disposed in front of the rear end31 b of the lower sheet 31.

In other words, the sheet composite 3 is so structured as to overlap theupper sheet 30 and the lower sheet 31 with the front and rear ends 30 a,30 b of the upper sheet 30 shifted relative to the front and rear ends31 a, 31 b of the lower sheet 31. Between the concave portions 2A and2B, a stepped surface 2Bb₁ is formed at the forefoot region F and astepped surface 2Bb₂ is formed at the heel region H.

In this case as well, in the same manner as the above-mentioned firstembodiment, the two-layer-structured sheet composite 3 composed of upperand lower sheets 30, 31 made of foamed rubber, i.e. a thickfoamed-rubber sheet layer, is disposed at the ball of the foot portionTE. Thereby, cushioning property can be improved at the ball of the footportion TE.

Also, at the toe portion, a single-layered sheet composite 3 composed ofonly the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubbersheet layer, is disposed. Thereby, a high repellent force can beobtained at the time of a push-off motion of the foot at the toeportion, and a propulsive force can thus be increased during exercises.

Moreover, the thin portion 2 e of the midsole body 2 is formed betweenthe frontmost end portion of the stepped surface 2Bb₁ and the uppersurface 20 of the midsole body 2. Therefore, when the foot pushes off atthe stepped surface 2Bb₁, a higher repellent force against the push-offforce of the foot can be obtained from the stepped surface 2Bb₁. As aresult, a higher propulsive force can be attained. Also, as foamedrubber composing the sheet composite 3, if the above-mentioned highrebounding rubber foam is used, a still higher rebounding force can beobtained and a much greater propulsive force can be attained.Furthermore, as the load is transferred from the heel rear end to theheel central portion, cushioning property is improved gradually or instages at the heel region H. In addition, the midsole body 2 is formedof foamed rubber, thus reducing the entire weight of the midsolestructure.

Third Embodiment

FIGS. 9 to 12 show a midsole structure for an athletic shoe according toa third embodiment of the present invention. In these drawings, likereference numbers indicate identical or functionally similar elements tothose in the first and second embodiments. In the first embodiment, anexample was shown in which the concave portions 2A, 2B that house thesheet composite 3 is open to the upper surface 20 and is not open to thelower surface 22 of the midsole body 2, and in the second embodiment, anexample was shown in which the concave portions 2A, 2B is open to thelower surface 22 and is not open to the upper surface 20 of the midsolebody 2.

In this third embodiment, the concave portions 2A and 2B are open toboth of the upper and lower surfaces 20, 22 of the midsole body 3. Also,in this third embodiment, the lower sheets 31, 31′ composing the sheetcomposite 2 do not extend from the heel region H through the midfootregion M to the forefoot region F. The lower sheets 30, 31 are separatedfrom each other in the longitudinal direction.

The concave portions 2A, 2B penetrate the midsole body 2 in thethickness direction (see FIGS. 10, 11). The lower sheet 31 extends froma front-end portion of the midfoot region M to the mid portion of theforefoot region F. The front end 31 a ₁ of the lower sheet 31 faces thefront-end wall portion 2B₁ of the concave portion 2B and the rear end 31b ₁ of the lower sheet 31 faces the rear-end wall portion 2B₂ of theconcave portion 2B. The lower sheet 31′ is disposed at the heel regionH. The front end 31 a ₂ of the lower sheet 31′ faces the front-end wallportion 2B₁′ of the concave portion 2B and the rear end 31 b ₂ of thelower sheet 30 faces the rear-end wall portion 2B₂′ of the concaveportion 2B. The lower surface 30B.of the upper sheet 30 is in contactwith the upper surface 31A of the lower sheet 31 and the upper surface31′A of the upper sheet 31′.

The front end 30 a of the upper sheet 30 is disposed in front of thefront end 31 a ₁ of the lower sheet 31 and the rear end 30 b of theupper sheet 30 is disposed at the rear of the rear end 31 b ₂ of thelower sheet 31′. At a region extending from the front end portion of theheel region H to the front end portion of the midfoot region M, thelower sheet is not provided and only the upper sheet 30 is provided.Between the concave portions 2A and 2B, a stepped surface 2Ab₁ is formedat the forefoot region F, a stepped surface 2Ab₂ is formed at the heelregion H, and a stepped surface 2Ab₃ is formed at the midfoot region M.

In this case as well, in a similar manner to the above-mentioned firstand second embodiments, the two-layer-structured sheet composite 3composed of upper and lower sheets 30, 31 made of foamed rubber, i.e. athick foamed-rubber sheet layer, is disposed at the ball of the footportion TE. Thereby, a touch on the foot and cushioning property can beimproved at the ball of the foot portion TE.

Also, at the toe portion, a single-layered sheet composite 3 composed ofonly the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubbersheet layer, is disposed. Thereby, a high repellent force can beobtained at the time of a push-off motion of the foot at the toeportion, and a propulsive force can thus be increased during exercises.

Moreover, the thin portion 2 e of the midsole body 2 is formed betweenthe frontmost end portion of the stepped surface 2Ab₁ and the lowersurface 22 of the midsole body 2. Therefore, when the foot pushes off atthe stepped surface 2Ab₁, a higher repellent force against the push-offforce of the foot can be obtained from the stepped surface 2Ab₁. As aresult, a higher propulsive force can be attained. Also, as foamedrubber composing the sheet composite 3, if the above-mentioned highrebounding rubber foam is used, a still higher rebounding force can beobtained and a much greater propulsive force can be attained.Furthermore, as the load is transferred from the heel rear end to theheel central portion and also the load is transferred from the midfootregion M to the forefoot region F, a touch on the foot and cushioningproperty can be improved gradually or in stages. In addition, since themidsole body 2 is formed of foamed rubber, the entire weight of themidsole structure can be reduced.

Fourth Embodiment

FIGS. 13 to 16 show a midsole structure for an athletic shoe accordingto a fourth embodiment of the present invention. In these drawings, likereference numbers indicate identical or functionally similar elements tothose in the first to third embodiments. In this fourth embodiment, anexample is shown in which the concave portions 2A, 2B that house thesheet composite 3 are open to neither the upper surface 20 nor the lowersurface 22 of the midsole body 2. That is, in this case, the upper andlower sheets 30, 31 that constitute the sheet composite 3 are housed inan interior space formed in the midsole body 2.

As shown in FIGS. 14 to 16, the midsole body 2 includes an upper midsole2 ₁ disposed on the upper side and a lower midsole 2 ₂ disposed on thelower side. The upper sheet 30 is housed in the concave portion 2Aformed on the lower surface 22 ₁ of the upper midsole body 2 ₁ and thelower sheets 31, 31′ are housed in two concave portions 2B formed on theupper surface 22 ₂ of the lower midsole 2 ₂.

In this case too, in a similar manner to the above-mentioned first tothird embodiments, the two-layer-structured sheet composite 3 composedof upper and lower sheets 30, 31 made of foamed rubber, i.e. a thickfoamed-rubber sheet layer, is disposed at the ball of the foot portionTE, such that thereby a touch on the foot and cushioning property can beimproved at the ball of the foot portion TE.

Also, at the toe portion, a single-layered sheet composite 3 composed ofonly the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubbersheet layer is disposed. Thereby, a high repellent force can be obtainedat the time of a push-off motion of the foot at the toe portion, and apropulsive force can thus be increased during exercises.

Moreover, the thin portion 2 e of the midsole body 2 is formed betweenthe frontmost end portion of the stepped surface 2Bb 1 and the lowersurface 22 of the midsole body 2. Therefore, when the foot pushes off atthe stepped surface 2Bb₁, a higher repellent force against the push-offforce of the foot can be obtained from the stepped surface 2Bb₁. As aresult, a higher propulsive force can be attained. Also, as foamedrubber composing the sheet composite 3, by adopting the above-mentionedhigh rebounding rubber foam, a still higher rebounding force can beobtained and a much greater propulsive force can be attained.Furthermore, as the load is transferred from the heel rear end to theheel central portion and also the load is transferred from the midfootregion M to the forefoot region F, cushioning property is improvedgradually or in stages. In addition, since the midsole body 2 is formedof foamed rubber, the entire weight of the midsole structure can bereduced.

Fifth Embodiment

FIGS. 17 to 20 show a midsole structure for an athletic shoe accordingto a fifth embodiment of the present invention. In these drawings, likereference numbers indicate identical or functionally similar elements tothose in the first to fourth embodiments. In this fifth embodiment, theconcave portions 2A, 2B that house the sheet composite 3 are disposed ata region from the front end portion of the midfoot region M to themidportion of the forefoot region F of the midsole body 2, i.e. mainlyat the forefoot region F. The concave portion is not provided at theheel region H. Therefore, the upper sheet 30 and the lower sheet 31 thatcompose the sheet composite 3 are disposed at the region from the frontend portion of the midfoot region M to the midportion of the forefootregion F of the midsole body 2, i.e. mainly at the forefoot region F.

In this case as well, similar to the above-mentioned first to fourthembodiments, the two-layer-structured sheet composite 3 composed ofupper and lower sheets 30, 31 made of foamed rubber, i.e. a thickfoamed-rubber sheet layer, is disposed at the ball of the foot portionTE. Thereby, a touch on the foot and cushioning property can be improvedat the ball of the foot portion TE.

Also, at the toe portion, a single-layered sheet composite 3 composed ofonly the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubbersheet layer, is disposed. Thereby, a high repellent force can beobtained at the time of a push-off motion of the foot at the toeportion, and a propulsive force can thus be increased during exercises.

Moreover, the thin portion 2 e of the midsole body 2 is formed betweenthe frontmost end portion of the stepped surface 2Ab₁ and the lowersurface 22 of the midsole body 2. Therefore, when the foot pushes off atthe stepped surface 2Ab₁, a higher repellent force against the push-offforce of the foot can be obtained from the stepped surface 2Ab₁. As aresult, a higher propulsive force can be attained. Also, as foamedrubber composing the sheet composite 3, by employing the above-mentionedhigh rebounding rubber foam, a still higher rebounding force can beobtained and a much greater propulsive force can be attained. Inaddition, since the midsole body 2 is formed of foamed rubber, theentire weight of the midsole structure can be reduced.

Sixth Embodiment

FIGS. 21 to 24 show a midsole structure for an athletic shoe accordingto a sixth embodiment of the present invention. In these drawings, likereference numbers indicate identical or functionally similar elements tothose in the first to fifth embodiments. In this sixth embodiment, theconcave portions 2A, 2B that house the sheet composite 3 are separatedmainly at the forefoot region F and the heel region H. Thereby, theupper sheets 30 are separated mainly at the forefoot region F and theheel region H and similarly the lower sheets 31 are separated mainly atthe forefoot region F and the heel region H.

In more details, the lower sheet 31 is disposed in the midportion of theheel region H and at the rear side part of the forefoot region F. At theheel region H, the rear end of the upper sheet 30 is disposed at therear of the rear end of the lower sheet 31 and the front end of theupper sheet 30 is disposed in front of the front end of the lower sheet31. Similarly, in a region from the midfoot region M to the forefootregion F, the rear end of the upper sheet 30 is disposed at the rear ofthe rear end of the lower sheet 31, and the front end of the upper sheet30 is disposed in front of the front end of the lower sheet 31.

In this case as well, as with the above-mentioned first to sixthembodiments, the two-layer-structured sheet composite 3 composed ofupper and lower sheets 30, 31 made of foamed rubber, i.e. a thickfoamed-rubber sheet layer, is disposed at the ball of the foot portionTE, such that thereby a touch on the foot and cushioning property can beimproved at the ball of the foot portion TE.

At the toe portion, a single-layered sheet composite 3 composed of onlythe upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubbersheet layer, is disposed, such that thereby a high repellent force canbe obtained at the time of a push-off motion of the foot at the toeportion and a propulsive force can thus be increased during exercises.

Moreover, the thin portion 2 e of the midsole body 2 is formed betweenthe frontmost end portion of the stepped surface 2Ab₁ and the lowersurface 22 of the midsole body 2. Therefore, when the foot pushes off atthe stepped surface 2Ab₁, a higher repellent force against the push-offforce of the foot can be obtained from the stepped surface 2Ab₁. As aresult, a higher propulsive force can be attained. Also, as foamedrubber composing the sheet composite 3, by adopting the above-mentionedhigh rebounding rubber foam, a still higher rebounding force can beobtained and a much greater propulsive force can be attained.Furthermore, as the load is transferred from the heel rear end to theheel central portion at the heel region H and also the load istransferred from the midfoot region M to the forefoot region F, a touchon the foot and cushioning property is improved gradually or in stages.In addition, since the midsole body 2 is formed of foamed rubber, theentire weight of the midsole structure can be reduced.

Seventh Embodiment

FIGS. 25 to 28 show a midsole structure for an athletic shoe accordingto a seventh embodiment of the present invention. In these drawings,like reference numbers indicate identical or functionally similarelements to those in the first to sixth embodiments. In this seventhembodiment, similar to the fifth embodiment shown in FIGS. 17 to 20, theconcave portions 2A, 2B that house the sheet composite 3 are disposed ata region from the front end portion of the midfoot region M to the midportion of the forefoot region F of the midsole body 2, i.e. mainly atthe forefoot region F. Therefore, the upper sheet 30 and the lower sheet31 that compose the sheet composite 3 are disposed at the region fromthe front end portion of the midfoot region M to the midportion of theforefoot region F of the midsole body 2, i.e. mainly at the forefootregion F.

However, this seventh embodiment differs from the fifth embodiment inthat the width of the concave portion 2B of the seventh embodiment issmaller than the width of the concave portion 2B of the fifth embodiment(see FIGS. 25, 27 and FIGS. 17, 19). The width of the concave portion 2Bis also smaller than the width of the concave portion 2A. On the medialside of the midsole body 2, the medial side surface 31 c of the concaveportion 2B is vertically aligned with the medial side surface 30 c ofthe concave portion 2A (see FIG. 27), but on the lateral side of themidsole body 2, the lateral side surface 31 c of the concave portion 2Bis not vertically aligned with and disposed laterally inwardly from thelateral side surface 30 c of the concave portion 2A (see FIG. 27).

In this case as well, similar to the above-mentioned first to sixthembodiments, the two-layer-structured sheet composite 3 composed ofupper and lower sheets 30, 31 made of foamed rubber, i.e. a thickfoamed-rubber sheet layer, is disposed at the ball of the foot portionTE, such that thereby a touch on the foot and cushioning property can beimproved at the ball of the foot portion TE.

At the toe portion, a single-layered sheet composite 3 composed of onlythe upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubbersheet layer, is disposed, such that thereby a high repellent force canbe obtained at the time of a push-off motion of the foot at the toeportion and a propulsive force can thus be increased during exercises.

Moreover, the thin portion 2 e of the midsole body 2 is formed betweenthe frontmost end portion, of the stepped surface 2Ab₁ and the lowersurface 22 of the midsole body 2 (see FIG. 26). Therefore, when the footpushes off at the stepped surface 2Ab₁, a higher repellent force againstthe push-off force of the foot can be obtained from the stepped surface2Ab₁. As a result, a higher propulsive force can be attained. Also, asfoamed rubber composing the sheet composite 3, by adopting theabove-mentioned high rebounding rubber foam, a still higher reboundingforce can be obtained and a much greater propulsive force can beattained. Furthermore, in this embodiment, from the lateral side to themedial side of the forefoot region F, a touch on the foot and cushioningproperty is improved gradually or in stages. Conversely, on the lateralside of the forefoot region F, a higher repulsive force can be attained,thus preventing supination during running. In addition, since themidsole body 2 is formed of foamed rubber, the entire weight of themidsole structure can be reduced.

Eighth Embodiment

In each of the above-mentioned first to seventh embodiments, an examplewas shown in which the midsole structure of the present invention wasapplied to a running shoe, but the application of the present inventionis not limited to such an example. The present invention also hasapplication to various sports shoes such as walking shoes, tennis shoes,indoor shoes and the like. The present invention is also applicable tocleated shoes or spike shoes such as soccer shoes, baseball shoes andthe like.

FIGS. 29 to 32 show a midsole structure for an athletic shoe accordingto an eighth embodiment of the present invention. In these drawings,like reference numbers indicate identical or functionally similarelements to those in the first to seventh embodiments. In this eighthembodiment, an example is shown in which the midsole structure 2 of thefirst embodiment is applied to a cleated shoe. Therefore, the midsolestructure 2 of the eighth embodiment is functionally similar to themidsole structure 2 of the first embodiment, and thus the eighthembodiment has similar effects to those of the first embodiment with theexception that a plurality of cleats are provided on the bottom surfaceof the outsole 4. In this eighth embodiment too, by the thicktwo-layer-structured sheet composite 3 made of foamed rubber, an upwardthrust from cleats 40 can be relieved with a favorable touch on the footand cushioning property maintained at the ball of the foot portion TE.Also, a propulsion force can be further increased during exercises bythe cleats provided directly below the stepped surface 2Ab₁.

Variant

In the above-mentioned first to eighth embodiments, an example was shownin which the sheet composite 3 has a two-layer structure that comprisesthe upper sheet 30 and the lower sheet 31, but the application of thepresent invention is not limited to such an example. The sheet composite3 may have a multiple-layer structure that comprises three or moresheets.

As mentioned above, the present invention is useful for a midsolestructure for an athletic shoe that can improve cushioning propertiesand a touch on the foot and that can enhance a propulsion force duringexercises.

Those skilled in the art to which the invention pertains may makemodifications and other embodiments employing the principles of thisinvention without departing from its spirit or essential characteristicsparticularly upon considering the foregoing teachings. The describedembodiments and examples are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. Consequently, while the invention has been described withreference to particular embodiments and examples, modifications ofstructure, sequence, materials and the like would be apparent to thoseskilled in the art, yet fall within the scope of the invention.

What is claimed is:
 1. A midsole structure for an athletic shoecomprising: a midsole body that is made of foamed synthetic resin; and asheet composite extending at least from a ball of a foot portion to atoe portion in said midsole body and comprising a plurality of foamedrubber sheets that are overlapped and shifted in a longitudinaldirection, wherein said sheet composite includes a single sheet at saidtoe portion and a plurality of sheets at said ball of the foot portion.2. The midsole structure according to claim 1, wherein said midsole bodyincludes a stepped concave portion that is open to afoot-sole-contact-surface side and that has a difference in level in thelongitudinal direction, and said sheet composite is housed in saidconcave portion.
 3. The midsole structure according to claim 1, whereinsaid midsole body includes a stepped concave portion that is open to aground-contact-surface side and that has a difference in level in thelongitudinal direction, and said sheet composite is housed in saidconcave portion.
 4. The midsole structure according to claim 1, whereinsaid midsole body includes a stepped concave portion that passes throughsaid midsole body in a thickness direction and that has a difference inlevel in the longitudinal direction, and said sheet composite is housedin said concave portion.
 5. The midsole structure according to claim 1,wherein said midsole body includes a stepped inner space that has adifference in level in the longitudinal direction and said sheetcomposite is housed in said inner space.
 6. The midsole structureaccording to claim 1, wherein said sheet composite is disposed at aforefoot portion of said midsole body.
 7. The midsole structureaccording to claim 6, wherein said sheet composite is disposed at a heelportion of said midsole body.
 8. The midsole structure according toclaim 1, wherein said sheet composite extends from a heel portionthrough a midfoot portion to a forefoot portion of said midsole body. 9.The midsole structure according to claim 7, wherein said sheet compositethat is disposed at said heel portion of said midsole body is separatedin the longitudinal direction from said sheet composite that is disposedat said forefoot portion of said midsole body.
 10. A midsole structurefor an athletic shoe comprising: a midsole body that is made of foamedsynthetic resin; and a sheet composite extending at least from a ball ofa foot portion to a toe portion in said midsole body and comprising afirst sheet and a second sheet that are made of foamed rubber and thatare overlapped and shifted in a longitudinal direction, each of saidfirst sheet and said second sheet having a front end disposed on a frontside thereof and a rear end disposed on a rear side thereof in thelongitudinal direction, wherein said front end of said first sheet islocated in front of said front end of said second sheet at said toeportion of said midsole body.
 11. The midsole structure according toclaim 10, wherein said front end of said first sheet contacts saidmidsole body from above.
 12. The midsole structure according to claim10, wherein said rear end of said first sheet extends to the rear ofsaid rear end of said second sheet.
 13. The midsole structure accordingto claim 10, wherein said first sheet is disposed at a forefoot portionand a heel portion of said midsole body and said second sheet comprisesa forefoot sheet portion disposed at said forefoot portion of saidmidsole body and a heel sheet portion disposed at said heel portion ofsaid midsole body, said forefoot sheet portion and said heel sheetportion are separated from each other in the longitudinal direction.